1. Field of Invention
The invention relates to methods for detection and characterization of semiconductor material defects. In particular, methods for isolation of semiconductor wafer support-related defects are provided using scanning infrared depolarization.
2. Description of Related Art
Semiconductor materials, such as silicon or GaAs, are used to make components, such as integrated circuits. Typically, these are formed from a moncrystalline semiconductor material in the shape of a wafer sliced from a silicon crystal ingot. This wafer is then subjected to several processing steps to form a final product. However, in order to be suitable for further upstream processing, the semiconductor material must be entirely or substantially free of crystal defects. Such defects may include, for example, dislocations, cracks, microflaws, sliplines, scratches, foreign particulate matter, and the like. These defects may be part of the original formed crystal structure, or may be induced by the various processing, handling and treatment steps.
Various methods and apparatus for detection of such crystal defects have been used. Early methods of crystal defect detection included microscopic detection, Raman scattering, photoluminescence or x-ray topography. However, these techniques were time consuming, required expensive equipment, and typically provided information on only a very small area of the wafer. More recent developments include Scanning Infrared Depolarization (SIRD).
Silicon and GaAs are optically isotropic cubic materials. Detection of defects in such materials can be found by looking at the mechanical stress field using the photoelastic effect of such materials. That is, stress in such materials cause optical anisotrophy and the refractive index of the material becomes a tensor of the applied stress. As a result, only light with defined polarization directions collinear with two principle axes of the cut ellipse of the refractive index tensor may propagate through the crystal. These two beams, the ordinary and extraordinary beam, travel with different speeds and cause an optical bifringence effect that effectively relates to the anisotrophy or amount of stress present. The phase shift between the two beams can be determined by analyzing the depolarization of the original polarized light after penetration through the wafer using a transmission polarimeter. By scanning a wafer surface with normally incident light, one can provide a non-destructive evaluation method for imaging of wafer crystal defects.
Such a method is faster, and provides full wafer mapping capability. However, most efforts have been expended at identification of crystal defects of a particular semiconductor wafer, without much focus on the source of the defects.
Wafer supports are used to support the semiconductor wafer at various stages of wafer processing. One example of a wafer support is a susceptor, commonly used in the formation of an epitaxial layer on the wafer through epitaxial growth. During such a process, a semiconductor wafer of a certain diameter, such as 100-400 mm, is placed on a susceptor suitably shaped to support the wafer. The wafer and wafer support (susceptor) are then placed in a controlled furnace environment containing a growth atmosphere, such as hydrogen gas. During the growth process, a reaction gas containing silicon is injected into the furnace and a resultant silicon epitaxial layer becomes deposited by reduction or thermal decomposition on the surface of the wafer. The wafer is then removed and subsequently processed. These wafer supports (susceptors) can induce defects into the semiconductor wafers for various reasons. These supports may be defective as designed, constructed, or fabricated. They may also become damaged during use or maintenance, or become damaged or defective due to improper assembly.
Wafers processed using the defective or damaged wafer support can have defects such as slip or stress, leading to breaking in the wafer manufacturing process or downstream customer processes. However, often times, the defective or damaged support is not discovered until large quantities of wafers have been processed on the defective support. The resultant cost of lost product, troubleshooting and resolving of customer claims can cost hundreds of thousands of dollars.
While general techniques have been able to identify several types of crystal defects, such methods have not been fully used to identify or provide quality control analysis of crystal defects attributable to wafer support-related defects. This is because there can be many sources or causes of the defects. Basic monitoring of wafers for monitoring of quality control parameters may identify defects, but does not automatically identify those defects attributable to wafer support problems. Instead, they generally reflect a quality problem with the particular wafer itself.
There is a need for a measurement and quality control monitoring process that can readily measure processed wafers and isolate wafer support-related defects so that proper adjustment, redesign or replacement of the wafer support can occur to prevent such large outlays of cash resulting from defective wafer formation.
The inventive SIRD measurement techniques allow quick and easy characterization of depolarization stress defects across an entire wafer. One such method of SIRD measurement of wafers is performed at least twice to isolate wafer support-related defects and determine whether wafer support quality is acceptable and does not introduce stress-related defects. Support-related defects may cause a localized stress in the wafer in the vicinity of the wafer support defect. By isolating defects caused solely by wafer support defects, the identification and location of such defects on the wafer can be used to ascertain the problem wafer support defect location, allowing for quality control through either repair, adjustment, redesign or replacement of the wafer support.
An exemplary embodiment of one such method of SIRD measurement of wafers to isolate wafer support-related defects involves SIRD measurement of multiple processed wafers, each oriented differently on the wafer support. Repetitive defects on multiple wafers at same orientations relative to the wafer notch, flat, or any other alignment feature used in wafer processing, can be discounted as pre-existing or pre-processing defects. Similarly, defects on wafers processed lasermark down (inverted) that are a mirror image to defects on wafers processed lasermark up can also be discounted as pre-existing or pre-processing defects. However, defects that change location relative to the notch/flat, but correlated to the orientation relative to the wafer support/susceptor can be isolated as wafer support-related defects. Analysis of such wafer support-related defects may then be used to identify and correct the corresponding wafer support defect.
A more particular exemplary method of characterizing depolarization stress defects on semiconductor wafers using Scanning Infrared Polarization (SIRD), comprises: mounting a first semiconductor wafer on a wafer support in a first orientation; performing a processing operation on the first semiconductor wafer while being mounted on the wafer support; removing the first semiconductor wafer from the wafer support; performing a SIRD scan of the first semiconductor wafer to obtain first wafer defect information; mounting at least one second semiconductor wafer on the wafer support in a different orientation than the first orientation; performing a processing operation on the at least one second semiconductor wafer while being mounted on the wafer support; removing the at least one second semiconductor wafer from the wafer support; performing a SIRD scan of the at least one second semiconductor wafer to obtain at least one second wafer defect information; correlating the first and at least one second wafer defect information to isolate orientation dependent defects from non-orientation dependent defects; and characterizing the orientation dependent defects as wafer support-related defects.
The second, different orientation may be upside down from the first orientation.
The process may use a plurality of second semiconductor wafers, each oriented differently.
The second, different orientation may be rotationally shifted relative to the first orientation.
The second wafer need not be different from the first wafer, but may be the same as the first wafer only oriented differently from the first orientation.
Once the wafer support-related defects are characterized and isolated, the obtained positional information can be used to remedy the wafer support defect.